1. Field of the Invention
The present invention relates to processes for the fabrication of acoustic probes comprising a set of emitting and/or receiving elements obtained by cutting from a large-sized transducer block. Such probes are especially used at the present time in applications such as echography.
2. Discussion of the Background
The invention relates more particularly to the means allowing the electrical connections to be made between the transducer elements and the electronic devices which are connected thereto. It makes it easier to fabricate transducers having a large number of elements arranged in particular in a two-dimensional arrangement.
Among the known connection techniques for two-dimensional echography probes is a process described by the Applicant in the French patent application published under No. 2,702,309, which proposes the use of a thin polymer film laminated to a metallized piezoelectric ceramic.
According to this prior art, vias are then collectively machined in the film at the position of the individual transducers to be interconnected. The connections are then made by lines etched in a metal layer deposited on the film and in the vias.
These lines are produced within the ceramic and on its periphery, and a flat connection means is therefore used on the surface of the ceramic, extended by a flexible connection means which can be bent over the edges of the ceramic in order to minimize the space taken up.
Such a process makes it possible to produce an acoustically discrete connection means which is able to conform to geometries that are sometimes complex (probes that are curved and of small size). Nevertheless, the step of producing the fine tracks with a fine spacing is carried out on an end-of-process product, and therefore one having a high added value, and having critical track-etching regions at the transition between flexible parts (flex) and rigid parts (ceramic).
In order to alleviate these drawbacks, the invention proposes a connection technique using a circuit of the dielectric-film type on which the interconnection lines are produced before assembly on the active elements of the probe. As will be explained later, this circuit may advantageously comprise interconnection lines on both sides.
More specifically, the subject of the invention is a process for the fabrication of an acoustic probe comprising an interconnection circuit and individual transducers produced in a plate of piezoelectric material which includes metallizations relating to the individual transducers, characterized in that it comprises the following steps:
production of conducting tracks on at least one side of a dielectric film (11, 21, 31);
bonding of the said dielectric film having conducting tracks to a layer (13, 23, 33) of piezoelectric material which includes metallizations, using a layer of dielectric adhesive (12, 22, 32);
production of vias through the dielectric film (11, 21, 31) and the layer of dielectric adhesive (12, 22, 32) by means of a suitable localization process so as to produce, simultaneously, vias which emerge, on the one hand, on a conducting track and, on the other hand, on an associated metallization;
production of electrical contacts between a conducting track (PI, PI1, PI2) and the metallization of the associated piezoelectric material (mi).
According to a first embodiment of the invention, the suitable localization process may be the focusing of an ablation laser.
According to a second embodiment of the invention, the suitable localization process may comprise the use of a mask.
According to one embodiment of the invention, the conducting tracks are produced on the lower side of the dielectric film, the layer of adhesive being in contact with this lower side and the layer of piezoelectric material. According to this embodiment, a metal mask may advantageously be produced, on the surface of the dielectric film, for the next step of etching the vias.
It is also possible to use an independent mechanical mask.
In general, the electrical contact between a conducting track and the metallization of the associated piezoelectric material is obtained by localized deposition of a conductive material, which may be a metal layer etched by masking or a conductive resin.
According to one embodiment, the electrical contact between a conducting track and the metallization of the associated piezoelectric material may be obtained by successive depositions of a metallization layer and of a layer of masking resin, followed by etching in order to leave the metallization layer only within the vias.
According to another embodiment of the invention, the upper side of the dielectric film comprises metal tracks. In this case, the etching may advantageously be carried out through a mechanical mask after having covered the upper side comprising the conducting tracts with a resin. After the vias have been etched, the step of producing the electrical contact between a conducting track and the metallization of the associated piezoelectric material may be carried out be depositing a layer of metal, followed by etching in order to leave the conducting layer only at the bottom of the vias, as will be explained below.
In general, the electrical contacts may be connected up by filling in the vias with a conductive resin, rather than by depositing a metallization layer and then by etching this layer.